Shear bond strength of composite, glass ionomer and acidic primer adhesivesystems

The purpose of this study was to determine the shear bond strengths of orth odontic brackets bonded with one of three methods: (I) a glass ionomer adhe sive with a 20% polyacrylic acid enamel conditioner; (2) a composite resin adhesive used with 37% phosphoric acid etchant and a conventional primer; o r (3) the same composite resin used with an acidic primer that combines the etchant with the primer in one application. The brackets were bonded to th e teeth according to one of three protocols. Group I teeth were etched with 37% phosphoric acid and bonded with Transbond XT (3M Unitek, Monrovia, Cal if) following the manufacturer's instructions. Group I acted as the control group. Group II teeth were etched with an acidic primer (Clearfil Liner Bo nd 2. J.C. Moritta Kuraway, Japan) that contains both the acid (Phenyl-P) a nd the primer (HEMA and dimethacrylate) and was placed on the enamel for 30 seconds; the adhesive used to bond the brackets was Transbond XT as in Gro up I. Group III teeth were etched with 20% polyacrylic acid and the bracket s were bonded with Fuji Bond LC (G.C. America, Chicago, III). A steer rod w ith one flattened end was attached to the crosshead of a Zwick test machine (Zwick GmbH & Co, Ulm, Germany). An occlusogingival load was applied to th e bracket, producing a shear force at the bracket-tooth interface. The resu lts indicated that the resin/phosphoric acid adhesive system (control group ) provided the strongest shear bond strength (x) over bar = 10.4 +/- 2.8 MP a). The glass ionomer adhesive system provided a significantly lower bond s trength ((x) over bar = 6.5 +/- 1.9 MPa). The least shear bond strength was present when the acidic primer was used with an orthodontic adhesive ((x) over bar = 2.8 +/- 1.9 MPa). In the present study, the use of either a fluo ride-releasing grass ionomer or an acidic primer in combination with an ava ilable orthodontic composite adhesive resulted in a significantly reduced s hear bond strength when compared with that of the conventional composite re sin adhesive system. At the present time, the orthodontist and the patient are better served by using phosphoric acid/composite resin adhesive system or other equivalent systems that provide a clinically reliable bond strengt h between the bracket, the adhesive, and the enamel surface.